The passage of small and large radiolabeled molecules with and without Evan's blue marker from blood to brain has been investigated in order to elucidate the blood-brain barrier permeability and its relationship to the development of ischemic cerebral edema. This investigation is still in progress. The preliminary results are as $ follows: (a) Long-term ischemic gerbils subjected to cerebral ischemia of 3 hours and 15 minutes recovery period showed only an increase in sucrose and dextrose values in the affected hemisphere whenever extravasation of Evan's blue albumin complex was seen in the cerebral tissue. Three hours after reestablishment of cerebral circulation following ischemia of 3 hours duration, the cerebral levels of dextrose were found increased only in animals with increased BBB permeability to Evan's blue. However, the cerebral sucrose levels were increased irrespective of presence or absence of increased permeability blood-brain barrier to Evan's blue. (b) So far, RISA was investigated only in short-term ischemia of 1 hour and various recovery periods showing an increased level after 20 hours of recovery in two out of six animals.